tools/mm/page_owner_sort: fix timestamp comparison for stable sorting

tools/mm/page_owner_sort: fix timestamp comparison for stable sorting

The ternary operator in compare_ts() returns 1 when timestamps are equal,
causing unstable sorting behavior. Replace with explicit three-way
comparison that returns 0 for equal timestamps, ensuring stable qsort
ordering and consistent output.

Link: https://lkml.kernel.org/r/20251209044552.3396468-1-kaushlendra.kumar@intel.com
Fixes: 8f9c447e2e2b ("tools/vm/page_owner_sort.c: support sorting pid and time")
Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
Cc: Chongxi Zhao <zhaochongxi2019@email.szu.edu.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>